At the weekend, hundreds of people in Warrington observed a minute's silence as 20 peace doves were released at a moving civic event to commemorate the bombing, which tore through the Cheshire town's shopping centre. Johnathan Ball (3) died instantly.

Tim died of his injuries five days later.

A further 56 people were injured by the two bombs which were placed in litter bins in Bridge Street and exploded shortly after midday that sunny Saturday, the day before Mother's Day.

No warning was given and nobody has ever been prosecuted for the outrage.

Colin and Wendy Parry stood near the spot where their son was fatally injured.

Mr Parry said 20 years ago two IRA members had "calmly, clinically and coldy" walked down the street planting two bombs, knowing innocent men, women and children out shopping would be the victims.

"The men who murdered these innocent victims were never caught and never will be," he said. "But quite possibly they may be listening today and may realise the futility of their actions here in Warrington. It did not further their cause but it did further the cause of peace."

The couple set up the Tim Parry Johnathan Ball Foundation for Peace, which has since become an internationally recognised centre for conflict resolution and victim support.

It is now called Survivors For Peace and offers support to victims and those affected by any form of conflict. The couple will address a lunch at Parliament Buildings describing the foundation's work and how Survivors for Peace could be incorporated into the planned development of a Peace Centre in Northern Ireland.

Mr Parry said: "We know that many people in Northern Ireland have been affected by political violence and we welcome this opportunity to again reach out our hand of friendship to the people of Northern Ireland and to update the Assembly members."

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"This town has made a difference, a real unique difference. Had things been different, Tim and Jonathan might well have walked where we are now, hand in hand with their own children, now but instead let's hope they are looking down saying 'well done Warrington'."